Authorities say they have recovered about 3,500 pieces of art that were illegally trafficked in Europe.

Spanish Civil Guard

Seventy-five people have been arrested across Europe for allegedly trafficking stolen art and archaeological relics, according to Spanish police who led the investigation.

Interpol and the U.N.'s culture agency, UNESCO, helped in the investigation, as did the European policing agency Europol and the World Customs Organization, according to a statement by UNESCO.

The statement noted the arrests took place back in November, but were not made public until late last week. Neither Spanish authorities nor the international bodies involved in the investigation said why they had not previously disclosed the arrests.

Lauren Frayer reported for NPR from Madrid:

"Spanish police say the suspects are members of criminal gang that trafficked stolen art and archaeological relics. They have been under investigation for months, by law enforcement from 18 countries, led by Spain and Cyprus.

"Altogether, police say they have recovered about 3,500 pieces of stolen art — including Byzantine relics and an Ottoman tombstone in Greece. Among those found in Spain were 19 artifacts stolen from an archaeology museum three years ago. Police have not issued a complete inventory, but said most of the artifacts were taken from countries at war."